1. Field of the Invention
The present invention relates to an image forming apparatus that forms a fixed image by heating and pressurization after toner is selectively attached to a latent image by a difference in electrostatic potential and a toner image is formed and this toner image is transferred to a recording material.
2. Description of the Related Art
A method in which after a toner image is directly transferred on a recording material electrostatically or after a toner image is primarily transferred to an intermediate transfer body and then is secondarily transferred to a recording material, toner including a thermoplastic resin binder is heated and melted and is fixed to the recording material has been widely adopted in a process for fixing a toner image in an image forming apparatus using powdery toner. This heating fixing method is a method in which a recording material on which an unfixed toner image is carried is passed through a nip part in which a pressurizing member and a fixing rotation body having a heating source are contacted and pressed and the toner image is heated and pressurized to perform fixing, and has advantages that fixing can be performed at low electric power and also there is a small danger of ignition due to a paper jam at a fixing part, so that the heating fixing method is widest used.
Such a fixing rotation body has a hollow core of, for example, aluminum and a heater disposed inside the core, and a roll-shaped member etc. whose surface is coated with fluorine resin are used in order to improve release characteristics. Also, a roll-shaped member in which an elastic layer is disposed on a metal core and its surface layer is coated with a fluorine resin tube etc. having good release characteristics is often used as the pressurizing member.
However, when a recording material on which an unfixed toner image is carried passes through a nip part between a pressurizing member and a fixing rotation body, a phenomenon in which toner transfers on a surface of the fixing rotation body, that is, an offset may occur. This offset toner adheres to a recording material next transported and the recording material is stained or a defect in an image is caused.
In order to solve the problem as described above, a roller cleaner is proposed.
Also, an apparatus for applying a voltage between the fixing rotation body and a pressurizing member and forming an electric field so that toner having an electric charge does not transfer to the fixing rotation body is known.
However, as one cause of offsetting toner to a heating rotation body, the fact that paper dust adhering to the fixing rotation body induces an offset was found newly. With this, means for effectively preventing an offset resulting from the paper dust is desired.
In recent years, use of recycled paper has been increasing from the standpoint of forest resources conservation or global environment conservation. Also, use of inferior paper (called “low-cost paper”) has been increasing in order to reduce cost of recording materials. The recycled paper or the low-cost paper has a large amount of paper dust adhering in a detachable state and when the recycled paper or the low-cost paper is used in an image forming apparatus, a portion of the paper dust may adhere to the fixing rotation body. Particularly, in the case of fixing an image having many non-image portions in which an image density is low and toner does not transfer, paper dust present in the non-image portions tends to adhere to the fixing rotation body. Then, when a subsequent recording material on which unfixed toner is carried passes through a pressure contact part between the fixing rotation body and a pressurizing member, the unfixed toner transfers to the paper dust adhering to this fixing rotation body and an offset of the toner to the fixing rotation body is caused. That is, the offset of the toner is induced by the paper dust adhering to the fixing rotation body and a stain on an image occurs frequently.